Question 1

How many rolls of wallpaper do I need?

Accepted Answer

Divide the room perimeter by the roll width to get the number of strips, then work out how many full strips each roll yields and divide. A 12 × 12 ft room with 8 ft walls and a plain paper typically takes 5 double rolls.

Question 2

How does a pattern repeat change the quantity?

Accepted Answer

Every strip has to start at the same point in the pattern, so each is cut to the next whole multiple of the repeat. With an 8 ft wall and a 21-inch repeat, each strip is cut at 8 ft 9 in — nine inches wasted per strip, which is why a large repeat can add 20–30%.

Question 3

What is the difference between a single and a double roll?

Accepted Answer

Almost all wallpaper is manufactured and sold as double rolls even though it is priced per single roll. A double roll is about 33 ft long, which yields four 8 ft strips; a single roll would yield only two.

Question 4

Should I subtract windows and doors?

Accepted Answer

Only large ones. A standard window does not save you a strip, because the strip above and below it still comes off the roll. Deduct only openings bigger than about 20 square feet, such as a patio door or a wide archway.

Question 5

How much extra wallpaper should I buy?

Accepted Answer

Order one extra roll beyond the calculation and keep it. Dye lots vary between print runs, so a roll bought a year later to patch a damaged strip will not match, no matter how carefully you order the same pattern.

Question 6

What is a straight match versus a drop match?

Accepted Answer

A straight match repeats horizontally, so adjacent strips are hung at the same height. A drop match offsets each strip by half the repeat, which uses slightly more paper but often reads better on a wall.

Question 7

How do I measure a room with a sloped ceiling?

Accepted Answer

Split the wall into a rectangle and a triangle. Calculate the rectangle normally, then treat the sloped section as full-height strips — you will cut the angle on site and the offcuts are rarely reusable.

Question 8

Can I wallpaper over existing wallpaper?

Accepted Answer

It is possible but not advised. The moisture in the new adhesive can loosen the old paper, and any seam or texture underneath telegraphs through. Strip it, wash off the residue, and prime before hanging.

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